DESCRIPTION: For more than a century, heart disease has been one of the most devastating health care issues facing the Western world, and is the single leading killer in America. Because the capacity for cardiac muscle to repair itself appears to be minimal at best, cardiac patients are often left with permanent damage that compromises pump function and deteriorates to a chronic state of heart failure. The associated economic cost of heart disease in the US alone is expected to exceed $250 billion dollars in 2006. Therefore, there has recently been tremendous excitement about novel cell-based approaches for replacing, repairing or regenerating damaged myocardium. However, the practical benefit of such strategies has been obscured by inconsistent results and very low survival rates of implanted cell grafts. The success of these techniques has been limited by a lack of control and understanding of the underlying mechanisms involved. This is partly due to a missing link in the available experimental methods. Success in the petri dish does not ensure translation to the animal model, and testing in animal models often involves such a complex combination of factors that it is difficult to interpret the outcomes. One approach that has been central to the study of cardiac muscle physiology is the use of isolated organ or tissue preparations. However, viability is limited to a few hours or days at best, which is insufficient to test a long term healing response. Clearly, the understanding of heart disease and mechanisms of repair would benefit from a simplified heart model that could be created in a tissue culture laboratory for high throughput in vitro testing. Therefore, the overall objective of this proposal is to use the principles of tissue engineering to create the first simplified heart chamber, or cardiac organoid, that exhibits the essential characteristics of ventricular pump function and can serve as an idealized surrogate heart for efficient evaluation of novel therapeutic strategies in vitro. By allowing independent control of chamber geometry, tissue composition, circulating biochemical factors, and mechanical loading conditions, this system would offer an unprecedented ability to study the effects of modulating a myocardial niche environment. Unlike more traditional cardiac patches or strips, the engineered tissue chamber would allow direct measurement of relevant functional relationships between pressure and volume that ultimately characterize the heart as a pump. Key aspects of this proposal are considered to be exploratory and developmental in nature, consistent with the objectives of the R21 funding mechanism. The overall objective will be achieved with the following specific aims: Aim 1: To develop a versatile high-throughput integrated bioreactor system for the creation, stimulation, and evaluation of engineered cardiac tissue chambers. Aim 2: To test the effects of mechanical and biochemical factors on the key structural, functional, and molecular features of engineered cardiac tissue chambers (ETCH). In particular we will test the hypothesis that wall stress modulates the interaction between human mesenchymal precursor cells and neonatal rat cardiac myocytes in ETCH co-cultures. [unreadable] [unreadable] [unreadable]